Electronic feedback control system for slow-speed operation of electromechanical devices

ABSTRACT

An electromechanical device comprising a driving coil and an armature responsive thereto is operated at a controllably slow speed by sensing the movement of the armature with a sensing coil responsive to magnetic flux changes between said driving coil and said armature and by degeneratively feeding back the voltage developed in the sensing coil to oppose or partially negate the driving voltage applied to said driving coil.

United States Patent [1 1 Myers Apr. 9, 1974 [54] ELECTRONIC FEEDBACK CONTROL 3,671,814 6/1972 Dicb 317/D1G. 6 S S O SLOW SPEED OPERATION 3,296,498 1/1967 Chassanoff et a1. 3 l7/D1G. 6

0F ELECTROMECHANICAL DEVICES 3,576,473 4/1971 Genbauffe et a1. 317/155.5

Inventor: John L. Myers, Dayton, Ohio Assignee: Ledex 1nc., Dayton, Ohio Filed: Oct. 13, 1972 Appl. No.: 297,185

US. Cl. 3'17/123, 317/D1G. 4 Int. Cl. 1101b 47/02 Field of Search 3l7/155.5, DIG. 4, DIG. 6,

References Cited 7 "UNITED STATES PATENTS 2/1965 G oldstein 3l7/l55.5 3/1964 Marchall 3l7/D1G. 6

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Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr.

Attorney, Agent, or Firm-Dybvig & Dybvig 57 ABSTRACT An electromechanical device comprising a driving coil and an armature responsive thereto is operated at a controllably slow speed by sensing the movement of the armature with a sensing coil responsive to magnetic flux changes between said driving coil and said armature and by degeneratively feeding back the voltage developed in the sensing coil to oppose or partially negate the driving voltage applied to said driving coil.

14 Claims, 3 Drawing Figures 1 ELECTRONIC FEEDBACK CONTROL SYSTEM FOR SLOW-SPEED OPERATION OF ELECTROMECHANICAL DEVICES BACKGROUND THE INVENTION 1. Field of the Invention This invention relates generally to circuits for controllably moving the armature of an electromechanical actuator device, and more particularly, to such a circuit which controls the speed at which the actuator operates as well as the noise produced by such operation.

2. Description of the Prior Art In numerous electromechanical actuator circuits, it has been the practice to provide two coils operatively associated with a single armature. Ordinarily, one of the two coils is a driving coil which causes the armature to move to produce useful work. Sometimes the second coil is a smaller coil capable of operating at a smaller power level for the purpose of holding the armature in the position in which it has done its work. In other cases, the second coil is employed to sense the movement of the armature and initiate secondary functions such as the operation of a switch in timed relation to the armature movement. In still other cases, the second coil is included in a regenerative feedback circuit which allows the power supplied to drive the armature to be substantially reduced after armature movement has commenced.

SUMMARY OF THE INVENTION In the present invention, two coils are operatively associated with a single armature. One coil functions as a driving coil to cause movement of the armature and the second coil functions as a sensing coil which senses the movement of the armature, the circuitry departing from prior art by utilizing a degenerative feedback which opposes or partially negates the driving power initially made available to the driving coil.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 isa schematic view illustrating electric circuitry embodying the present invention.

FIG. 2 is a schematic view of apparatus suitable for use in conjunction with the circuitryof FIG. 1.

FIG. 3 is a cross-section view more particularly illustrating a device suitable for operation in conjunction with the circuitry of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT I FIG. 2 illustrates an armature which is preferably ferromagnetic. The armature is responsive to an electromagnetic driving force developed by-means of a solenoid coil 12. The coil 12 is so wound as to enclose a cylindrical space into which the armature 10, also a cylinder, will move axially upon energization of the coil develops a voltage across its terminals 17 and 19 which is proportional to the time rate of change in the flux associated with the coil 12.

As previously mentioned, it is known in the prior art to connect the terminals of a sensing coil such as the coil 14 in a feedback circuit in such fashion that the electromotive force generated across the terminals 17 and 19 is returned to the coil 12, either with or without current and/or voltage amplification to increase the current flowing through the coil 12, thereby allowing a reduction in the current and/or voltage applied to the terminals 13 and 15 to sustain the magnetic field about the coil 12. This type of feedback connection between the coils 12 and 14 is known as a regenerative feedback, the feedback being regenerative in the sense that it tends to sustain or augment the existing current through the coil 12 and thus perpetuate or increase the magnetic field aboutthe coil 12. In the practice of the present invention, feedback is also used; but the feedback is more accurately characterized as a degenerative feedback because it opposes or negates the current condition which is creating the magnetic field attracting the armature 10.

In the practice of the present invention, it is important, for reasons to be described, to observe the sense in which the coils l2 and 14 are wound; but it is unimportant whether the coils are wound in the same sense or in the opposite sense.

Referring to the circuit of FIG. 1, the coil 12 with its terminals 13 and 15 appears in the lower right of F IG. 1. Above the coil 12 is a mark 12a indicating that the coil 12 is energized by connecting theterminal 15 positive with respect to the terminal 13. The coil 14 also appears in FIG. 1 and has a mark 14a adjacent its upper end. The function of this mark is to signify that when the armature 10 moves into the coil 12, flux increase between the armature 10 and the coil 12 will cause the terminal 17 to become positive relative to the terminal 19. This can result because the two coils were wound in the same sense. It can also result, however, if the two coils were wound in the opposite sense, one from the other, and if the terminals 17 and 19 have been interchanged. The purpose of the marks 12a and 14a is thus to show that the polarity of the terminal 17 relative to the terminal 19 is the same as the polarity of the terminal 15 relative to the terminal 13 when the armature 10 is advancing into the coil 12.

In the circuit of FIG. 1, the conductor 18b is maintained at ground potential by a ground connection shown at 18a. Likewise, a conductor 16b is maintained at a uniform positive potential with respect to ground by application of a positive input voltage to a terminal 160.

The resistances 20 and 22 connected between the conductors 16b and 18b divide the input voltage so as to maintain a reference potential, at the junction 24, which is intermediate ground and the input voltage. The junction 24 serves as one input to a two-input differential amplifier 26. The differential amplifier is illustrated in schematic form and no attempt has been made to illustrate its common and well-understood bias connections.

Series-connected resistances 28, 30, 32 and a selected portion of the resistance of a potentiometer 36 having an adjustable tap 34 comprise a second voltage divider connected between the conductors 16b and 18b. This second voltage divider establishes a second voltage at a junction 35 which voltage is applied through conductor 42 to a second amplifier input 43. The input 43 is commonly referred to as the inverting input or the summing point. I

The resistance 32 is a variable resistance which'is adjusted, before initiating circuit operation, to equalize the voltages at the junctions 35 and 24 such that there 26 to its the junction 35. The voltages at the junctions 24 and 35 being no longer substantially equal, and the voltage at junction 24 being the higher, the differential amplifier 26 outputs a positive voltage to its output 27. This voltage is applied through a resistance 44 in series with a Zener diode 46 to the base 48 of a transistor 50. The transistor 50 has a collector 52 connected to the positive voltage conductor 16b and an emitter 54 connected through a resistance 56 to the ground conductor 18b.

The Zener diode 46 functions primarily to block any off-set voltage from the amplifier 26.

Assuming the amplifier output to havebeen dropped to substantially zero by adjustment of the variable resistance 32 and assuming, thereafter, that the switch 40 has been closed, the circuit is designed to produce'a sufficient voltage difference at the inputs to the differential amplifier 26 to generate an output at the amplifier output 27 which is sufficient to produce conduction through the Zener diode 46 and drive the transistor 50 to a conductive state.

A fraction of the input voltage will therefore appear voltage at junction 24. The development of the feedback voltage on the potentiometer 36 had the effect of driving the junction 35 more positive, thus reducing or subtracting from the voltage difference between he junctions 24 and 35, and thus reducing the output of at the junction 57 and thus be applied to the base 58 of a second transistor 60. The transistor 60 has a collector 62 connected to the positive input conductor 16b and an emitter 64 connected through the inductance coil 12 to the ground conductor. 18b. With the transistor 50 in a conductive state, the passage of current through the emitter 64 of the transistor 60 to ground through the inductance coil 12, places the transistor 60 in a conductive state such that a large fraction of the input voltage is supplied to the coil 12. The transistors 50 and 60 thus operate as a power driver responsive to the output of the amplifier 26. This power driver taken in combination with the amplifier 26 may be referred to as a power control means for the coil 12.

Having reference to FIG.2 this energization of the coil 12 initiates an advance of the armature 10 into the coil 12. As well known, the movement of the armature 10 into the coil 12 results in a flux change which induces a voltage in the coil 14 proportional to the velocity of armature motion. The coils 12 and 14 are so linked that this flux change causes the terminal 17 to become positive relative to the terminal 19. The positive voltage at the terminal 17 is dropped to ground through the resistance of potentiometer 36, and a frac-. tion of this voltage determined by the setting of the potentiometer 36 is fed back to the summing input 43 of the amplifier 26.

the differential amplifier 26. The feedback can thus be called subtractive or degenerative. As a result of the feedback, the conductivity of the transistors and 60 is reduced. The consequence is that the voltage across the coil 12 is reduced and the rate of build-up of a magnetic field about the coil 12 is retarded. As a further result, the magnetic attraction for the armature 10 increases at a slower rate than would have taken place in the absence of the degenerative feedback. Since there is less attraction for the armature 10 as a result of the feedback, the velocity with which the armature 10 moves into the coil 12 is reduced in comparison to the case that would have existed in the absence of the feedback.

Those skilled in the art will realize that the foregoing discussion is not to be interpreted as meaning that the feedback is reducing the current through the coil 12 in an absolute sense. Rather, the feedback is reducing the rate of current increase through the coil 12 as the armature moves into the coil 12.

The extent to which feedback from the coil 14 can be used to reduce the velocity of the armature motion through the coil 12 is determined primarily by the setting of the potentiometer 36. Thus, if the potentiometer tap 34 is moved downwardly, as it appears in FIG. 1, the feedback is reduced with the result that the velocity of movement of the armature 10 will be permitted to increase. Likewise, as the tap 34 is moved upwardly, as it appears in FIG. 1, the feedback is increased and the velocity of armature movement reduced. By reason of the circuitry described, it has been found possible to slow an armature movement which would normally occurin a fraction of a second toan armature movement occurring over a period of several seconds, thus substantially reducing the kinetic energy present in the armature 10 when it completes its advance into the coil 12.

As in any feedback system, stability mustbe considered. It has been found in practice that distributed capacitance between the drive coil 12 and the feedback coil 14 can cause a high frequency instability. To combat such instability, a capacitance 70 is connected be- It will be noted that the closing of the switch 40 which initiatedthe armature motion'had the effect of making the voltage at junction 35 less positive than the tween the amplifieroutput 27 and the amplifier input 43. The resistance 72 also connected between the amplifier output 27 and the amplifier input 43 is a conventional gainsetting resistor.

The diode 68 placed across the coil 12 serves primarily to provide arc suppression should the field about the coil 12 be collapsed abruptly, as by interruption in the source of power. Those skilled in the art will realize, of course, that the circuitry of the present invention not only retards the development of a magnetic field about the coil 12, but, by reason of the feedback circuitry described, will also retard the collapse of a magnetic field about the coil 12. Accordingly, the diode 68 is ordinarily not important for are suppression except in cases of abnormal circuit operation.

FIG. 3 illustrates one type of solenoid device in which the present feedback circuit can be used to obvious advantage. The device comprises a ferromagnetic casing sized to receive a driver coil and a sensing coil 140. The coils encircle a non-magnetic sleeve 82 which guides the movement of a cylindrical ferromagnetic armature 84.

The coils 120 and 140 are series connected and have a lead 130 connected at the junction between the two coils. Additional leads 150 and 170 connect to the opposite ends of the series connected coils. Having reference to FIGS. 1 and 2, the lead 170 thus corresponds to the previously described coil terminal 17. The lead 150 likewise corresponds to the previously described coil terminal 15. It can be noted also that the lead 130 corresponds to the previously described coil terminal 13 and, as shown in FIG. 1, the coil terminals 13 and 19 when connected into the control circuitry are electrically common. Thus the lead 130 is electrically the same as the coil terminal 19 when assembled into the circuitry of FIG. 1.

A first ferromagnetic fitting 85 encloses one end of the casing 80 and provides a support for the sleeve 82. A second ferromagnetic fitting 86 encloses the opposite end of the sleeve 82 with clearance for the leads 130, 150 and 170 and also supports the opposite end of the sleeve 82. The fitting 86 has a conical recess 87 which serves to provide a narrow air gap for the armature 84 as the armature reaches its innermost travel.

Seated in an armature groove, not shown, is a split spring ring 88 which retains an adjacent non-magnetic spacer 90. The function of the spacer 90 is to stop armature movement by engaging the fitting 85 before the armature physically contacts the fitting 86. In the absence of the feedback circuit described in FIGS. 1 and 2, the armature 84 will fully enter the casing 80 within a fraction of a second following energization of the coil 120. Obviously, when the armature 84 enters the casing 80 in only a fraction of a second, the spacer 90 will slam against the fitting 85, producing a clearly audible noise at the moment of impact and causing a substantial transfer of kinetic energy from the armature 84 to the casing 80. When the coils 120 and 140 have been substituted into the FIG. 1 circuit to replace the previously described coils 12 and 14, however, a proper setting of the potentiometer 36 can be made such that the armature 84 slowly enters the casing 80 and the spacer 90 strikes the fitting 85 with only a barely audible noise and a barely noticeable transfer of kinetic energy to the casing 80.

Those skilled in the art will quickly recognize that with the aid of the feedback circuitry described, the noise generated by operation of the electromagnetic device and the shock transferred from the armature to the casing 80 become factors within the control of the user of the solenoid device. By merely adjusting the potentiometer 36, the user can thus reduce the noise and shock from operation of the device to whatever level is acceptable to his needs.

It is to be noted that the control circuitry of the present invention operates without sacrifice in the capability of the electromagnetic device to do work. Thus when the armature 84 is acting against a load such as may be attached to the bore 92, the armature 84, if stopped by the load, will receive full power, provided, of course, that the switch 40 remains closed. In other words, whatever power can be initially supplied to the coil 120 by closure of the switch 40 is restored to the coil 120 at any time armature motion should stop while the switch 40 remains closed.

In one manner of use of the present circuit, the switch 40 may be a push-button switch which is held closed by an operator until the work to be performed by the armature 84 has been completed. At any time the armature 84 slows or stops prior to the time the desired work has been completed, the feedback circuitry of the present invention will increase the current supplied to the coil 120, as needed, up to the maximum current initially made available to the coil upon closure of the switch 40.

Although preferred embodiment of the invention has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. In combination with an electromechanical device having a driving coil, an armature, one of said driving coil and armature movable relative to the other, and a sensing coil flux-linked to said driving coil; a source of direct current voltage, a control circuit including power control means connected in series with said driving coil across said voltage source, said power control means having a summing input, the power passed to said driving coil by said control means being determined by the voltage applied to said summing input, said control circuit including initiator means coupled to said voltage source and said summing input to apply a direct current voltage to said input for initiating a power supply to said driving coil, and feedback means coupling the voltage developed by said sensing coil to said summing input in opposition to the voltage applied by said initiator means whereby the power supplied to said driving coil is reduced as the rate of change of flux between said driving coil and said armature increases.

2. The combination of claim 1 wherein said power control means comprises an amplifier, and said summing input is an input to said amplifier.

3. The combination of claim 2 wherein said power control means further includes a power driver connected between the output of said amplifier and said driving coil.

4. The combination of claim 2 wherein'said amplifier is a differential amplifier having two inputs and one output, said summing input being one of said two amplifier inputs, said control circuit including means applying a reference voltage to the other of said two amplifier inputs.

5. The combination of claim 4 wherein said voltage developed by said sensing coil is coupled to said one amplifier input.

6. The combination of claim 5 wherein said means applying a voltage to said one amplifier input is a voltage divider including a resistance element, and said feedback comprises means connecting said sensing coil to said resistance element.

7. The combination of claim 6 including a potentiometer having a resistance member and a tap dividing said resistance member into two sections, one section being said resistance element and the other section includes in said means connecting said sensing coil to said voltage divider.

8. The combination of claim 4 wherein said initiator means comprises means to apply a voltage different than said reference voltage to said one amplifier input.

9. The combination of claim 8 wherein said means to apply a voltage different than said reference voltage in- 1 cludes a switch means for interrupting the application rect current power supply to aid driving coil, and

means coupling said sensing coil to said amplifier to provide degenerative feedback to said amplifier whereupon the power supply initiated by said amplifier decreases as the rate of change of flux between said driving coil'and said armature increases.

1 l. The combination of claim 10 in which said amplifier is a differential amplifier having two inputs and one output, said control circuit including means to apply areference voltage to one of said inputs, said voltage applied by said initiator means applied to the other of said inputs.

12. The combination fo claim 11 wherein said means coupling said sensing coil to said amplifier couples said sensing coilto said other input. t

13. The combination of claim 10 wherein said means coupling said amplifier to said driving coil includes diode means having a reverse bias breakdown potential serially connected between said amplifier and said driving coil.

14. In combination with an actuator device having a driving coil, an armature movably responsive to said driving coil, and a sensing coil flux-linked to said driving coil; a direct current voltage supply means, a control circuit including a differential amplifier having two inputs and one output, said control circuit including a first voltage divider connected to said voltage supply means applying a reference voltage to one of said inputs, said control circuit including a second voltage divider connected to said voltage supply means for applying a control voltage to the other of said inputs, means coupling said sensing coil to said second voltage divider, means coupling said driving coil to the output of said differential amplifier, command meanscoupled to said second voltage divider to produce at said other input a direct current control voltage different than said reference voltage thereby to initiate an output from said differential amplifier, driver means coupled to said voltage supply means and said driving coil and responsive to said output to supply power to said driving coil, said sensing coil so coupled to said second voltage divider as to reduce the difference between said control and reference voltages in response to the rate of flux increase between said armature and said driving coil.

-'UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2; 80? L56 Dated April 9, 197 -1 Inven oreQ John L. Meyers I It is certified that errorappears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 2, line 48. "t ee 0nd occurrence should read IN THE CLAIMS Column 6, Iliib 3, .C,.l a im, 'r'hibolude s" should read ---included---- ol n 7 li efi Q:-'C im,,1o.."ot" should read -to---t---- coi m 7,v l en; Cla: Im 1o, "aid" should read;- --saicI---- c lu line 29, cla 12,"'fo" should read Ori Signed and sealed this 10th day of December 1974 (SEAL) Attest:

' McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM'DC GUSTO-P69 UJ. OOVIIIIIIIY PIIIYING OFIICI IIII 0-!ll-J3l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,803, 56 Dated April 9, 97

InventorgQ John L. Meyers It is certified that error appears in the'sbove-i'dentified patent and that said Letters Patent are hereby corrected as shown below:

In column 2, line 8- 't second occurrence, should read IN THE CLAIMS Column 6, li! ..63;mC.l im7L7, "'iit'mludes should read ---inc1uded---- ol 7 lin 0 10,.'1'ot" should read ---to----- L Columrg 7, line Claim 10, "aid" should read: --said Colrlmnj, lirie 29, Claim l2, "fo should read --of Signed and sealed this 10th day of December 1974 (SEAL) Attest:

. MCCOY M. GIBSON'JR. I c. MARSHALL DANN 'Attesting Officer Commissioner of Patents FORM I USCOMM Dc 0031a P69 Q U... .OVIIIHII" PIIIIYING OFIICI "II 0-360-334 

1. In combination with an electromechanical device having a driving coil, an armature, one of said driving coil and armature movable relative to the other, and a sensing coil flux-linked to said driving coil; a source of direct current voltage, a control circuit including power control means connected in series with said driving coil across said voltage source, said power control means having a summing input, the power passed to said driving coil by said control means being determined by the voltage applied to said summing input, said control circuit including initiator means coupled to said voltage source and said summing input to apply a direct current voltage to said input for initiating a power supply to said driving coil, and feedback means coupling the voltage developed by said sensing coil to said summing input in opposition to the voltage applied by said initiator means whereby the power supplied to said driving coil is reduced as the rate of change of flux between said driving coil and said armature increases.
 2. The combination of claim 1 wherein said power control means comprises an amplifier, and said summing input is an input to said amplifier.
 3. The combination of claim 2 wherein Said power control means further includes a power driver connected between the output of said amplifier and said driving coil.
 4. The combination of claim 2 wherein said amplifier is a differential amplifier having two inputs and one output, said summing input being one of said two amplifier inputs, said control circuit including means applying a reference voltage to the other of said two amplifier inputs.
 5. The combination of claim 4 wherein said voltage developed by said sensing coil is coupled to said one amplifier input.
 6. The combination of claim 5 wherein said means applying a voltage to said one amplifier input is a voltage divider including a resistance element, and said feedback comprises means connecting said sensing coil to said resistance element.
 7. The combination of claim 6 including a potentiometer having a resistance member and a tap dividing said resistance member into two sections, one section being said resistance element and the other section includes in said means connecting said sensing coil to said voltage divider.
 8. The combination of claim 4 wherein said initiator means comprises means to apply a voltage different than said reference voltage to said one amplifier input.
 9. The combination of claim 8 wherein said means to apply a voltage different than said reference voltage includes a switch means for interrupting the application of said different voltage to said one input.
 10. In combination with an actuator device having a driving coil, an armature, one of said driving coil and armature movable relative to the other, and a sensing coil flux-linked ot said driving coil; a source of direct current voltage, power driver means connected in series with said driving coil across said voltage source, a control circuit including an amplifier and means coupling said amplifier to said power driver means, said control circuit including initiator means for applying a direct current voltage to said amplifier to initiate a direct current power supply to said driving coil, and means coupling said sensing coil to said amplifier to provide degenerative feedback to said amplifier whereupon the power supply initiated by said amplifier decreases as the rate of change of flux between said driving coil and said armature increases.
 11. The combination of claim 10 in which said amplifier is a differential amplifier having two inputs and one output, said control circuit including means to apply a reference voltage to one of said inputs, said voltage applied by said initiator means applied to the other of said inputs.
 12. The combination of claim 11 wherein said means coupling said sensing coil to said amplifier couples said sensing coil to said other input.
 13. The combination of claim 10 wherein said means coupling said amplifier to said driving coil includes diode means having a reverse bias breakdown potential serially connected between said amplifier and said driving coil.
 14. In combination with an actuator device having a driving coil, an armature movably responsive to said driving coil, and a sensing coil flux-linked to said driving coil; a direct current voltage supply means, a control circuit including a differential amplifier having two inputs and one output, said control circuit including a first voltage divider connected to said voltage supply means applying a reference voltage to one of said inputs, said control circuit including a second voltage divider connected to said voltage supply means for applying a control voltage to the other of said inputs, means coupling said sensing coil to said second voltage divider, means coupling said driving coil to the output of said differential amplifier, command means coupled to said second voltage divider to produce at said other input a direct current control voltage different than said reference voltage thereby to initiate an output from said differential amplifier, driver means coupled to said voltage supply means and said driving coil and responsive to said output to supply Power to said driving coil, said sensing coil so coupled to said second voltage divider as to reduce the difference between said control and reference voltages in response to the rate of flux increase between said armature and said driving coil. 